In compacting of soil, asphalt and similar materials with vibratory rollers, the vibration amplitude has proved to be of decisive importance for the compaction effect of the roller. An increase in amplitude normally increases the degree of compaction and also its depth effect, something which is true over the entire vibration frequency range. This is particularly the case for rubble, stony moraine and cohesive soils.
When the material being compacted becomes excessively hard, a vibratory roller may, however, begin to vibrate highly irregularly, whereupon the entire roller drum or parts thereof leave the surface of the ground. These vibrations are experienced as bouncing or asymmetric vibrations. In the event of such severe vibrations, the frame of the roller and the driver platform begin to shake and the rubber elements between the roller and frame are subjected to abnormal wear.
Normally, compaction of the material is not improved through the severely irregular vibrations and, in many cases, the degree of compaction will be reduced under the influence of excessively violent jolts against the ground by the roller.